Xanthan gum hydrophilic colloid is typically available as a food grade product as well as an industrial grade product, both being offered commercially as dry, white powders. The industrial grade xanthan gum hydrophilic colloid, or more simply xanthan gum, will exhibit different physical properties from the food grade product. Also, the food grade product should generally show excellent suppression of microbial growth.
Both grades have extraordinary resistance to enzymatic degradation. And in the dry, powdery form, even the industrial grade product is resistant to microbial growth. However it is recommended that aqueous solutions of the industrial grade product contain preservative. This recommendation is made if the xanthan gum solution is to be stored for a period longer than only 24 hours. Thus, the present invention is particularly directed to solutions of the industrial grade material.
A variety of well known preservative substances have been successfully used with the industrial grade xanthan gum solutions for retarding bacterial action. It would of course be economically desirable if the material were to be resistant to bacterial action without preservative, when it is otherwise advantageous to have the xanthan gum in solution, and when such solutions may be prepared more than 24 hours before use.
One of the uses of the industrial grade material, where it comes into contact with chromic acid, is in the preparation of coating compositions. For example it has been shown in U.S. Pat. No. 3,671,331 that coating compositions containing chromic acid and providing excellent corrosion resistance for metal substrates, can further desirably contain xanthan gum in the composition. This patent also teaches that it can be further desirable, such as prior to shipping and storage, to pre-package various composition ingredients. Subsequent blending is then used to prepare the coating composition.
Chromic acid, even in quite dilute aqueous solutions readily provides for such solutions being at a very low pH. For example as little as 0.25 weight percent of chromic acid in water will yield a solution pH of about 1.7. Further, chromic acid is a powerful oxidizing agent. The problems that can be encountered with solutions of xanthan gum and chromic acid are not unique to the gum since chromic acid is so voracious an oxidizer that it has well recognized incompatibility in aqueous solution with many industrial products.